Detection in quantitative measurement of the number of coliform bacteria present in water is frequently of vital importance for determining the effectiveness of water treatment processes in removing bacterial contamination. The presence in sewage of coliform bacteria make this organism a sensitive indicator of pollution. Coliform, along with other bacteria, are also quite readily removed from water by conventional water purification processes. The common intestinal bacteria pathogens are at least as susceptible to the artificial and natural purification processes to which water is subjected as is the more common coliform bacteria. Therefore, the coliform group may be employed as a good indicator of bacterial pollution.
As discussed in U.S. Pat. No. 4,204,037 (Dill et al), there are presently several methods known for the detection of coliform bacteria in aqueous solutions. These methods are generally divided into two classes of detection, both being based on the production of metabolic hydrogen liberated by the coliform organisms after inoculation into a lactose broth. One such method, disclosed in U.S. Pat. No. 3,907,646 (Wilkins et al), measures the increase in pressure due to metabolically produced hydrogen where the coliform bacteria are cultured in a hermetically sealed chamber. Another method, disclosed in U.S. Pat. No. 4,009,078 (Wilkins et al) utilizes a test tube containing two electrodes positioned in the growth nutrient broth containing coliform organisms. Hydrogen evolution is measured by an increase in voltage in a negative direction caused by the metabolic hydrogen production. In U.S. Pat. No. 4,204,037, an automated apparatus and method for detecting coliform organisms by measuring the increase in voltage caused by metabolic hydrogen in the growth medium is disclosed.
An apparatus and method for measuring the amount of gas absorbed or released by a substance has also been disclosed in U.S. Pat. No. 3,740,320 (Arthur). In the system disclosed in this patent, the air from the top of the closed chamber containing the water solution is circulated through a gas analyzer. The changes in a particular gas caused by the bacterial activity in the sample solution are determined by the gas analyzer. From this information, the activity of the bacteria in the solution is determined.
It has also been disclosed in the prior art that the quantitative determination of a particular type of volatile material in a liquid can be determined by first transferring the desired volatile to a liquid of known conductivity. The change in conductivity of the liquid to which the volatile material has been transferred indicates the quantitative amount of the volatile contained in the sample. A method and apparatus of this type is disclosed in U.S. Pat. No. 4,209,299 (Carlson).